Medullary thyroid cancer (MTC) is a neuroendocrine tumor and accounts for 3-5% of cases of thyroid cancer. The majority of patients with MTC do not present with early stage disease. Differentiated thyroid cancer (DTC) accounts for >90% of all thyroid cancers. In a sub-set of patients, thyroid cells become resistant to I-131 radioiodine therapy and subsequently develop distant metastases. In both MTC and DTC, systemic chemotherapy for metastatic disease is largely ineffective.